Photoactive/Passive Molecular Glass Blends: An Efficient Strategy to Optimize Azomaterials for Surface Relief Grating Inscription

Abstract

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (T). We prepare blends of a photoactive molecular glass functionalized with the azo Disperse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol % of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of T from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE, and initial inscription rate reach a maximum when T is 25-40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol % azo content, choosing the optimal T enables doubling the SRG inscription rate and increasing DE 6-fold. Moreover, a higher azo content enables higher DE for a similar T. Spectroscopy measurements indicate that the photo-orientation of DR1 and its thermal stability are maximal with T around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo-orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal T that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

Taming Macromolecules with Light: Lessons Learned from Vibrational Spectroscopy

“…[65] Recently, we have used PM-IRSAS to elucidate the T g dependence of photoorientation by mixing a DR1-containing molecular glass with various photopassive glasses. [73] We showed that the maximum orientation and the orientation stability, after the laser source is removed, are unaffected by the fraction of photoactive glass in the mixture at constant T g . The orientation and orientation stability both increase with T g up to an optimal value (60 °C for blends containing 40% of the photoactive glass) and then decrease and become constant, respectively, with further increase in the T g , which helps explain the complex T g dependence during the optical inscription of surface relief gratings.…”

“…For dispersed mixtures of the small molecule DR1 in different (isotactic, syndiotactic, and atactic) poly(methyl methacrylate)s, it was shown that the host polymer with the lowest glass transition temperature ( T g ) (60 °C) allowed the greatest DR1 mobility and thus the highest photo‐orientation . Recently, we have used PM‐IRSAS to elucidate the T g dependence of photo‐orientation by mixing a DR1‐containing molecular glass with various photopassive glasses . We showed that the maximum orientation and the orientation stability, after the laser source is removed, are unaffected by the fraction of photoactive glass in the mixture at constant T g .…”

“…The orientation and orientation stability both increase with T g up to an optimal value (60 °C for blends containing 40% of the photoactive glass) and then decrease and become constant, respectively, with further increase in the T g , which helps explain the complex T g dependence during the optical inscription of surface relief gratings. [73] Recent developments in molecular glass functionalization [74] may allow precise control of the molecular environment and thus enable a deeper understanding of photoinduced phenomena in azomaterials through IR investigations.…”

Driving Cells with Light‐Controlled Topographies

“…[18] Azobenzenes are among the most popular molecular photoswitches because of their ability to undergo a conformational change between two isomeric states when irradiated with UV or visible light. [25][26][27][28][29] When dealing with 2D light-responsive substrates, topographies can be instructed by a direct laser writing exposure of azopolymeric films previously spun on planar glass substrates. [25][26][27][28][29] When dealing with 2D light-responsive substrates, topographies can be instructed by a direct laser writing exposure of azopolymeric films previously spun on planar glass substrates.…”

Exploiting Anisotropy of Plasmonic Nanostructures with Polarization Modulation Infrared Linear Dichroism Microscopy (µPM‐IRLD)

“…Polarized light can be readily used to probe the orientation, and anisotropy of molecular systems, including thin films, proteins, and self‐assembled monolayers . When combined with microscopy, polarized light measurements can yield critical information about the orientation of crystallographic axes in microstructures or enable the ability to map the distribution of anisotropic domains .…”